1. Field of the Invention
This invention relates to a rotary roll-type rubber extruder for continuously extruding a rubber or rubberlike material, for example, a thermoplastic material, particularly rubber members such as rubber sheets required to form treads, sidewalls, rubber chafers, inner liners and the like by joining the rubber sheets into cylindrical forms.
2. Description of the Prior Art
In extruding rubbers or rubberlike materials, there is generally a tendency of the materials to expand in cross-section immediately after the extrusion. This is usually referred to as "swell" and further causes great shrink of the materials in the extruded direction. A new proposal has been therefore expected for many years, which is capable of producing ideal extruded rubberlike material which does not include residual strains and has high accuracy relative to a shape of a mouthpiece.
Screw-type extruders have also been widely used. Such a screw-type extruder comprises a screw extruding assembly provided on its front end with an die head having at an outlet a mouthpiece. Rubbers extruded from this type extruder are greatly likely to cause the swell, and often to cause tears in the form of saw-teeth in their side edges. These defects of the extruded rubbers make difficult design of mouthpieces.
A profile calender system has also been known, which comprises two parallel rolls, one of which is formed in its cylindrical surface with a notch to form with the other roll an opening corresponding to a predetermined section or contour of rubbers to be extruded. As disclosed in the literature, however, this system also tends to cause swells and extruded rubbers are likely to deform after they are extruded due to local differences in extruding speed resulting from differences in rotating radii of the rolls where the opening is formed. Moreover, the rolls used in this system are expensive to manufacture and troublesome to replace.
U.S. Pat. No. 3,871,810 discloses an improved screw-type extruder which comprises a single roller die disposed at a front end of a screw extruding assembly to increase pressure at an outlet of the roller die and emphasizes the effects of the improved extruder. However, it implies the following problems.
(1) Swells still occur and contours of mouthpieces must be determined by trial and error. PA0 (2) Natures and configurations of extruded rubbers are changed depending upon changes in extruding speed and rubber. PA0 (3) Dimensions of the extruded rubbers are affected by the variation in amount of extruded rubber on the side of the screw extruding assembly. PA0 (4) Extruded members often locally shrink and curve to obstruct a later tire building process. PA0 (5) There is a tendency for the rubber to be scorched in the die head. PA0 (6) In changing rubber materials to be extruded, troublesome and time-consuming work is required to remove residual rubber in the die head.
In order to solve the problems (2) and (4), particularly, the extruded rubbers must be forcedly extended and shrinked by setting complicated line speeds. For this purpose, however, it is required to provide additional installations and to elongate a length of conveyor line in the extruding train following to the extruding process or make the conveyor line into a multiple stage line.